You can use the DocumentServices.DocumentExporter class to easily export document contents. Here is some sample code for exporting the images for all documents in the search results:

for (int i = 1; i <= Results.RowCount; i++)
{
    int docid = (int)Results.GetDatum(i, SystemColumn.Id);
    EntryType eType = (EntryType)Results.GetDatum(i, SystemColumn.EntryType);

    if (eType == EntryType.Document)
    {
        DocumentInfo document = Document.GetDocumentInfo(docid, repo.Session);
        if (document.PageCount > 0)
        {
            using (PageInfoReader pageInfos = document.GetPageInfos())
            {
                foreach (PageInfo pageInfo in pageInfos)
                {
                    if (pageInfo.ImageDataSize > 0)
                    {
                        DocumentServices.DocumentExporter docExporter = new DocumentServices.DocumentExporter();
                        docExporter.PageFormat = DocumentServices.DocumentPageFormat.Png;

                        string imageFilePath = "c:\\temp\\" + document.Id.ToString() + "_" + pageInfo.PageNumber + ".png";
                        // to export directly to a file:
                        //docExporter.ExportPage(document, pageInfo.PageNumber, imageFilePath);

                        using (System.IO.FileStream fileStream = System.IO.File.Create(imageFilePath))
                        {
                            docExporter.ExportPage(document, pageInfo.PageNumber, fileStream);
                        }
                    }
                }
            }
        }
    }
}